1. Field of the Invention
This invention relates generally to data recording disk drives, like magnetic recording hard disk drives (HDDs), and more particularly to the disk stack assembly that is mounted for rotation on the disk drive spindle motor.
2. Description of the Related Art
In a magnetic recording hard disk drive (HDD) the recording disks are stacked on a disk stack assembly that is mounted to a disk drive spindle motor. The spindle motor is mounted to the disk drive base and rotates the disks about a central axis. An air-bearing slider that supports a magnetic recording read/write is associated with each disk surface. Each of the sliders is connected to a rotary actuator by a suspension and actuator arm. The actuator moves the sliders across their respective disk surfaces while an air-bearing, generated between the slider and its associated disk surface as the disks rotate, supports each slider in close proximity and near-contact with its associated disk surface.
The distance between the slider and its associated disk surface is called the “fly height”. While the fly height of each slider varies as a function of disk radius it is important that the fly height behavior of all the sliders be relatively predictable and consistent for all sliders across their associated disk surfaces. This requires that all the disk surfaces be as perfectly planar as possible.
The disk stack assembly includes a generally cylindrically shaped hub that is mounted to the spindle motor for rotation about the spindle motor's central axis. The hub includes a radially extending flange. The disks are stacked on the flange with spacer rings between them to allow the sliders to access their respective disk surfaces. A disk clamp is secured to the hub and clamps the stack of disks and spacer rings to the flange. The clamped disks in the disk stack assembly often exhibit “coning” or “cupping”, i.e., the disk surfaces have a slight conical shape instead of being perfectly planar. Coning is undesirable because it affects the fly height of the sliders and can prevent the sliders on different disk surfaces from having generally the same fly height behavior across their respective disk surfaces. As thinner disks come into use to accommodate the need for more compact disk drives, the coning effect becomes even more significant. The extent of coning is related to the amount of clamping force. Even if a disk stack assembly is designed with a supposedly optimum clamping force to minimize coning, it is difficult to control the clamping force to within a narrow range during manufacturing so that disk stack assemblies can be produced with unknown and possibly unacceptable coning.
What is needed is a disk stack assembly where the disks exhibit minimal coning and where the assembly can be manufactured without precise control of the clamping force.